The present invention relates to an image fiber capable of preventing the entrance of ambient light.
Among devices utilizing optical fibers is a fiberscope including an image fiber formed by bundling a plurality of optical fibers in a desired configuration and fusing them together into one body. One end of the image fiber is connected to an image-sensing section and the other end to an image-receiving section. Such a fiberscope can generally be used in the examination of confined places where direct examination is impossible. Also, a fiberscope can be used in the examination of locations where the surrounding atmosphere is dangerous, such as in the case of poisonous substances, locations where the temperature is very high, and locations exposed to nuclear radiation.
The structure of a typical fiberscope is shown in FIG. 1. Referring to FIG. 1, the fiberscope is composed of an image-sensing section 1, an image-receiving section 2, and an image-transmitting section 3. An object under the camera section 1 can be viewed through the transmitting section 3 using the image-receiving section 2. In order to illuminate the object being examined, a light guide 5 is connected to the image-receiving section 2. This light guide 5 passes through the transmitting section 3 and reaches the sensing section 1. The light guide 5 is made up of a plurality of plastic fibers 6.
The cross-section of the transmission section 3 is as shown in FIG. 2. In the transmission section 3, the image fiber 7 used to transmit an image from the image-sensing section 1 to the image-receiving section 2, a plurality of plastic fibers used to transmit light for illumination from a light source 4 to the image sensing section 1, and a filler 8 are surrounded by a coating 9. The image fiber 7 is fabricated by coating a bundle of optical fibers 10 with coating 11 of, for example, a silicone resin. The object being examined is illuminated with light from the light source 4 and is viewed with the image-receiving part 2.
Another transmission section structure as shown in FIG. 3 has been proposed. In this structure, a transparent plastic material, such as polymethyl methacrylate (PMNA), is extruded around an image fiber to form a light-transmitting portion 6'. This permits the fabrication of cables of unitary structure. Furthermore, the cross section of the cable is utilized with high efficiency, and transmission of light for illumination and an image can easily be accomplished. In this case, the coating 9 can be formed using an extrusion method.
Part of the light which is used for illumination and which is transmitted through the fiber 6 can get into the image fiber, for example, by reflection from scratches on the surface of the fibers and higher-mode leakage. This reduces the contrast of the field image.
The primary object of the invention is to overcome this problem and hence to provide an image fiber which does not allow the incidence of the light from the outside.